1. Field of the Invention
The invention relates to marine steering systems and, more particularly, relates to a steering system for a boat or other watercraft that is powered by a motor and steered by a tiller. Specifically, the invention relates to a tiller-operated steering system that is self-locking upon tiller release so as to immunize the tiller from reaction forces that would otherwise be imposed on the tiller by the motor or other steered element. The watercraft's steered element therefore retains the last steering angle commanded upon tiller release.
2. Discussion of the Related Art
In one type of conventional marine steering system, a watercraft such as a boat is steered by pivoting an outboard motor on the stem of the watercraft about a vertical steering axis under control of an operator. The steering forces are typically generated manually using a tiller that is located at the stem of the boat and that is connected to the motor either directly or indirectly via a mechanical steering linkage.
Reaction forces are imposed on and/or by the motor or other steered element during normal operation of the typical boat. These reaction forces may cause the steering angle to change unless the reaction forces are countered by the operator. The operator must therefore retain control of the tiller at all times in order to maintain a desired steering angle. The operator's freedom of movement therefore is sharply curtailed. In addition, the reaction forces increase generally proportionately with motor size. The relatively large reaction forces imposed on and by larger motors require commensurately larger retention forces by the operator, leading to operator fatigue over time.
Several proposals have been made to incorporate features into a marine steering system to prevent reaction or backlash forces imposed on or by the motor or other steered element from being translated back to the tiller. Most of these systems take the form of a wrapped spring brake or similar mechanical lock that acts on a steering shaft assembly or other rotational steering system component. The mechanical lock releases automatically when steering forces are imposed on one end of the rotational component so as to permit rotation of that component for the purpose of changing the steered element's steering angle. The lock engages automatically when backlash or reaction forces are transmitted to the opposite end of the rotational component, thereby locking the component from rotation and maintaining the last commanded steering angle of the steered element. Systems of this type are disclosed, for example, in U.S. Pat. No. 2,927,551 to Bevis; U.S. Pat. No. 2,947,278 to Magill; U.S. Pat. No. 3,039,420 to Bevis; and U.S. Pat. No. 3,796,292 to Harrison.
Others have proposed the coupling of a watercraft's steered mechanism to a hydraulic cylinder whose piston is locked from motion upon release of the steering mechanism so as to lock the rudder or other steered element in position and, thereby prevent backlash forces from being transmitted back to the steering mechanism. Systems of this type are disclosed, for example, in U.S. Pat. No. 3,631,833 to Shimanckas; U.S. Pat. No. 3,658,027 to Sturgis; U.S. Pat. No. 4,227,481 to Cox; and U.S. Pat. No. 4,557,695 to Neissen.
However, all of the self-locking steering systems described above are rather complex and cannot be easily installed without substantial modification to the existing steering system. Most of these systems are configured exclusively for use with a helm-based steering system rather than a tiller-based steering system. None is configured to be easily incorporated into an existing tiller-based steering design or retrofitted onto a pre-manufactured tiller-based steering system.
Perhaps as a result of these deficiencies, the prevailing approach used by engine manufacturers utilizes a friction based system, located between the tilt tube for an outboard engine and a tiller, and operable to resist tiller movement. The degree of resistance can be adjusted by manually adjusting a knob. While such friction-based devices reduce the transfer of forces on the tiller, they also hinder tiller operation. They also are necessarily limited in the capacity to block the tiller against undesired movement. They also tend to wear with time, requiring frequent readjustment to maintain the desired resistance.
The need therefore has arisen to provide a simple, effective, self-locking tiller operated power assist steering system that maintains a steering angle against reaction forces on or by the steered element, thereby negating the need for the operator to constantly man the tiller.
The need has additionally arisen to provide a self-locking system that can be incorporated into an existing tiller-based steering system with no more than minimal modification to the existing steering system design.